Conventionally, as a design method of an optical system, the steepest descent method, the conjugate gradient method, the least-squares method, etc. have been used. Each of these methods is called an optimization technique, and an evaluation function having two or more variables is used.
When these optimization techniques are used for a design of an optical system, what is equivalent to a variable of an evaluation function is an evaluation parameter (or an evaluation criteria), for example, such as aberrations and the like. This evaluation parameter is computed based on the value of the optical parameter (or composition) of optical systems, such as a radius of curvature of an optical action surface, a surface interval, and a refractive index. Therefore, if a value of the optical parameter of an optical system is changed, a value of an evaluation parameter changes, and change of the value of an evaluation parameter changes a value of an evaluation function.
Then, by changing gradually a value of an optical parameter of an optical system, processing for calculating the optimal value (for example, the minimum value and the minimal value) of an evaluation function is carried out.
Thus, when an optimal value of an evaluation function is obtained, an optical system having the optimal combination of a value of each optical parameter of the optical system at that time will be expressed. As a result, a value of an optical parameter of the optical system nearest to an intention of a designer is obtained. In addition, in case that an optimal value of an evaluation function is calculated, processing which an evaluation parameter also brings close to desired targeted value simultaneously is carried out.
In this way, in a design of an optical system, an optical parameter of the optical system that an evaluation function serves as the optimal value, and an evaluation parameter reaches in target tolerance level is determined.
For example, in order to reduce change of performance of an optical system by a production error adding some correction to a design value, and applying a limitation to the number of variables for optimization, etc. have been made. Such correction and limitation are carried out by a designer's own handwork. This handwork is carried out based on know-how and the like such as a design value obtained by computer, knowledge and experience of thea designer.
However, in recent years new design methods of an optical system have been proposed by, for example, Japanese published unexamined patent application Toku Kai Hei 11-30746, Japanese published unexamined patent application Toku Kai Hei 11-223764, Japanese published unexamined patent application Toku Kai Hei 11-223769, Patent No. 3006611, Japanese published unexamined patent application Toku Kai 2002-267926,etc.